This invention relates to a blank profile specifying method in automatic programming for lathes. More particularly, the invention relates to a blank profile specifying method well-suited for specifying the profile of a blank in cases where the blank has a special profile other than that of a cylinder or hollow cylinder.
Automatic programming systems for lathes have come into practical use and are used to create NC tapes from a design drawing through a simple operation by entering data in a conversational mode using a graphic display screen. With such an automatic programming system, a machining profile (exclusive of dimensions) can be entered merely by pressing profile symbol keys, which are located on an operator's panel, corresponding to a workpiece profile written on a design drawing. Further, according to the automatic programming system, referential information is graphically displayed on the screen from time to time and inquiries are made in ordinary language, so that dimensions and various data can be entered in response to the inquiries. When all data necessary for creation of an NC tape have been entered, the system immediately displays the blank profile and the finished profile, begins automatic calculation of NC command data and graphically displays a tool path to create an NC tape. A programming method performed by such an automatic programming system will now be described in detail. The method comprises the following steps:
(1) drawing mode selection step; PA1 (2) blank and blank dimensions input step; PA1 (3) machining profile and machining profile dimensions input step; PA1 (4) machine reference point and turret position input step; PA1 (5) process selection step; PA1 (6) tool selection step; PA1 (7) machining area and cutting conditions designation step; and PA1 (8) tool path calculation step.
The necessary data are entered successively to eventually create the NC tape. In the first step of selecting a drawing format, a coordinate system in line with the method of entry of the dimensions on the design drawing is selected from the information displayed on the graphic display screen. Specifically, four drawings indicative of drawing format and their menu numbers 1, 2, 3, 4 appear on the screen along with an inquiry calling for selection of a coordinate system. Keys on a keyboard are operated in response to the inquiry, and one of the keys is used to enter a menu number and, hence, select a coordinate system.
In the second step for entering a blank and the dimensions thereof, a picture for entering a blank profile and its dimensions appears on the graphic display screen, as shown in FIG. 1. While viewing the picture displayed, one enters the blank, its dimensional values L, D, D.sub.o, and the position of a base line ZP. Specifically, since the types of blank for turning are broadly classified into a cylinder, hollow cylinder and special profile (special blank), the images of these blanks and their menu numbers appear on the display screen, one of the blanks is selected from among the displayed blanks by entering its menu number, then, in accordance with inquiries calling for dimensional values, namely the length L, thickness D, bore diameter D.sub.o and base line ZP of the blank, these dimensions are entered via the keyboard. This completes the entry of the blank and dimensional values.
In the third step for entering machining profile and dimensions, (a) coordinate axes and the blank profile, as well as a machining profile inquiry, are displayed on the screen, and one responds to the inqury, while observing the design drawing, by pressing a profile symbol key on the keyboard in accordance with the profile on the design drawing, thus to enter the machining profile, and (b) following the entry of the machining profile, the display screen makes an inquiry requesting the necessary dimensions, and dimensions taken from the design drawing are entered from the keyboard in response to the inquiry, thereby completing the entry of a machining profile and its dimensions. A finished profile conforming to the entered machining profile and dimensions will appear on the graphic display screen.
In the fourth step for entering machine reference point and turret position, a drawing showing the positional relationship among the finished profile, turret and machine reference point is displayed together with an inquiry requesting a machine reference point and turret index position, which are necessary for creating NC data. The prescribed numerical values are entered from the keyboard in response to the inquiry to complete the entry of machine reference point and turret index position.
In the fifth step for process selection, a prescribed machining process is selected. Specifically, when a single part is to be machined by a lathe, the machining processes available include (a) center drilling, (b) drilling, (c) rough cutting of outer diameter, (d) rough cutting of inner diameter, (e) semi-finishing of outer diameter, (f) semi-finishing of inner diameter, (g) outer diameter finishing, (h) inner diameter finishing, (i) grooving and (j) threading. One of these machining processes is selected in the fifth step. To select a machining processing, one need only enter the name of the desired machining process, which is displayed on the display screen, by a menu number in response to an inquiry requesting which process is desired.
In the sixth step for selecting a tool, one responds to inquiries by entering the tool number of a tool to be used, a tool position compensation number, tool nose radius, virtual nose position, nose angle, etc.
In the seventh step for determining machining area and cutting conditions, one responds to inquiries on the screen by entering clearance, finishing allowance, depth of cut, retraction amount, cutting speed, feedrate, etc.
In the eighth step for calculating tool path, NC data indicative of tool path are obtained by using all of the data entered in the first through seventh steps, tool trajectory is displayed on the basis of the NC data, and the NC created are delivered as an output.
In an automatic programming method of this kind, there are cases where the blank entered in the second step is a special blank. In such cases an NC tape is created by taking it for granted that the uncut thickness of the special blank with respect to the finished profile along each of its axes is uniform. In other words, a special blank which will have a uniform uncut thickness along each of its axes with respect to a finished shape is prepared in advance. When the dimensions of this special blank are to be entered, data t.sub.x, t.sub.z indictive of the uncut thicknesses along the respective axes are entered, and a tool path is eventually calculated by using these data. FIG. 2 is a sectional view (showing only a first quadrant) of a finished profile 1 (solid line) and special blank profile 2 (dashed line). The uncut thickness t.sub.x along the X axis is constant throughout, and the same is true of the thickness t.sub.z along the Z axis. Points P.sub.1, P.sub.2... P.sub.5 are points of inflection.
Cast articles are often special blanks and in many cases do not have a uniform uncut thickness with respect to a final finished profile. Calculating the tool path is difficult when uncut thickness is non-uniform. For this reason, automatic programming in the prior art is performed by taking it for granted that uncut thickness is uniform. In actual machining, however, this results in idle cutting and prolonged machining time. Other prior-art methods include a method of automatic programming by specifying blank profile, and a method of cutting by assuming that a blank is a cylinder. However, the former method results in complicated programming because the blank profile cannot be specified simply, and the latter method results in idle cutting when actual machining is carried out.